In joint prostheses, centering devices or centralizers are used to position an implant stem, particularly femoral implant stems, within an operatively prepared intramedullary cavity. The centralizers position the implant stem so that the stem can be implanted into a bed of bone cement with a uniform thickness of cement surrounding its circumference. Often, a centralizer is used at both the proximal and distal ends of an implant stem. Centering devices are well known and have been developed in a variety of shapes and configurations. Typically, distal centralizers are configured to include a plurality of edges, barbs, or blades that press against or embed in the bone wall as the implant is driven into the intramedullary cavity. Generally, distal centralizers are attached to an implant stem by a post which is inserted or threaded into a bore formed in the stem's distal end, or by an opening in the centralizer which fits about the distal end of the stem. With implant stems which include a bore to receive a distal centralizer with a corresponding post, the bore does not typically fill with cement in the instance when a surgeon elects not to utilize the centralizer. An air bubble may thus expand into the cement creating a defect in the cement mantle. Accordingly, a filler peg is typically provided to fill the hole in the instance where the distal centralizer is not utilized.
Smith & Nephew Richard Inc. of Tennessee has developed an implant stem and distal centralizer that are connected using a tapered fit between the blades of the distal centralizer and the implant stem. The implant stem has two cross slots formed through the distal end of the stem in a cruciate configuration. The slots extend transversely across the width of the implant stem. The distal centralizer includes four blades which extend radially in a "plus sign" shaped configuration. The configuration of the blades allows the centralizer to be seated within the cross slots of the implant stem. In the instance where the surgeon elects not to utilize this distal centralizer, the transversely extending cross slots could provide a chance for an air bubble to form, if the cement does not fill the slots, which would not be desirable.